Method and apparatus for transferring loose material

ABSTRACT

The present invention concerns a method for transferring tree trunks or other loose material in a troughed conveyor by exerting to the material to be transferred abrasive forces acting sequentially in transfer direction and in return direction. The abrasive forces acting in the transfer direction are exerted to the material to be transferred simultaneously on both of the partial surfaces between the stationary centre portion and the stationary side surfaces. The abrasive forces acting in the return direction are exerted non-simultaneously as well with respect to the abrasive forces in the transfer direction as with each other. The invention further concerns a respective apparatus.

The present invention concerns a method for transferring solid materialin pieces or particles, for instance wood trunks, chip of bark in athrough-shaped conveyor by exerting to the material to be transferredsequentially abrasive forces in the transfer direction and in the returndirection on sub-areas of the through. The friction forces exerted tothe material to be transferred from the stationary surfaces of theconveyor are smaller than the abrasive forces acting simultaneously inthe transfer direction, but bigger than the abrasive forces acting inthe return direction.

The invention further concerns an apparatus for transferring solidmaterial in pieces or particles, such as tree trunks, chip, bark orother loose material, said apparatus comprising a stationary frame andparallel, longitudinal elements movable reciprocating in the transferdirection.

Recently it has been disclosed an apparatus in accordance with patentU.S. Pat. No. 5,063,981 and WO 00/40383 (F183181 and FI109103), whichhas turned out to be very practical for feeding pulpwood to a barkingdrum. The device in accordance with U.S. Pat. No. 5,063,981, however,requires a relatively great number of transfer elements. Practicallytransfer elements from 6 to 8 are needed, whereby the exact control oftheir movement is essential for the operation. The feeding device inaccordance with that invention for feeding pulpwood is equipped withbalk-like transfer elements supported on rolls. This has led to arelatively expensive construction comprising lots of components.

The device has later been improved so that the friction force betweenthe transfer elements and the material to be transferred is as constantas possible between the different transfer elements. Due to theoptimizing of this friction force exerted to the transfer elements, thenumber of the transfer elements could be decreased to four or even tothree. For this reason the construction costs of the device have beenconsiderably reduced. This kind of a construction is known from WO00/40383 (FI109103).

Common for the devices described in both of said publications is thatthe bottom of the conveyor as a whole is formed of movable transferelements. That means that with a device comprising three and five balksa relatively compact bottom and a conveyor not tipping refuse can beachieved.

The method in accordance with the present invention is characterized inby what has become apparent from the enclosed claim 1.

The transfer apparatus in accordance with the present invention ischaracterized in by what has become apparent from the enclosed claims 3and 4.

The present invention and its details will be described in more detailin the following, with reference to the enclosed drawings, wherein

FIG. 1 shows a traditional transfer apparatus known in the art;

FIG. 2 shows a transfer apparatus of prior art, equipped with threetransfer elements;

FIG. 3 shows a transfer apparatus of the present invention, equippedwith two transfer elements;

FIG. 4 shows a transfer apparatus of the present invention, equippedwith four transfer elements.

FIG. 1 shows a transfer device of prior art in accordance with patentsFI 83181 and U.S. Pat. No. 5,063,981, by means of which efficienttransfer of pulpwood bundles can be achieved with a troughed form of thetransfer bottom consisting of eight transfer elements 1. In a device inaccordance with FIG. 1, the loose mass moves forward with a uniformvelocity along with a majority of the bottom balks, and the balksperform a quick return movement one by one. Because the transfer devicesin accordance with FIG. 1 are of uphill type, and the friction of thematerial to be transferred against the side is disadvantageous, theside-most transfer elements 2 are in a steep angle of about 60° thusincreasing the movable side surface and decreasing the side friction.

The bottom of the transfer device consists of 6 equal, balk-liketransfer elements 1 having an equal climbing angle. Transfer balks 2 and2′ have been fixed to the sides 3 and 3′ of the device. The sides of thedevice are braced and supported by feet 4 and 4′ also supporting thebalk 5 having a form of a flat V. Roller supports 6 and rollers 7 aremounted on top of the same. Supporting balks 5 have been arranged at acertain distance from each other in the transfer direction of theapparatus. In the lateral direction the transfer balks 1 are supportedby lateral supporting rolls 8. The patent application of the apparatusdescribes the operation principle of an apparatus in accordance withFIG. 1 and how the logs 9 are bound by each other during the transport.

In a more advanced embodiment of WO 00/43383 and an apparatus of FIG. 2,the number of balk-like transfer elements has been decreased to three.That was achieved by rolling the side balks to a certain angle, whichhas increased the friction exerted thereto by the material to betransferred. As the operation conditions of the apparatus have beendisclosed in detail in said publication, they will not be dealt with inthis connection.

The centre transfer balk 10 is supported with two parallel supportingrolls 11 and 11′. The outermost transfer balks 13 and 13′ have beensupported with rolls 12 and 12′. The side guiding rolls 14 and 14′support the side balks and keep them in place.

The height of the sides 3 and 3′ of a transfer apparatus in accordancewith FIG. 2, or the loading height of the material, is chosen so thattheir common friction force is equal to the single friction force of onetransfer balk. In order to guarantee good operation, the apparatusrequires an adequate load and gives thereby good transport capacity evenwith a climbing angle of a couple of degrees.

FIG. 3 shows a transfer apparatus in accordance with the presentinvention comprising supporting feet 4 and 4′ for supporting the sides 3and 3′. Between the supporting feet there is provided a balk 20 andbracing corner plates 19 and 19′, rolls 12 and 12′ being supported fromthose by brackets 18. Movable transfer balks 13 and 13′ are placed ontop of the same. These are kept in place in the lateral direction bylateral guiding rolls 14 and 14′. In the centre of the apparatus thereis an immovable balk parallel to the transfer direction, being formed ofa plate 21 having a form of a flat V and of bracing 22.

The transfer apparatus in accordance with FIG. 3 operates periodicallylike the apparatus of FIG. 2. Thereby the material is transferredsequentially for a certain transfer distance by means of transferelements, after which the material to be transferred stops and thetransfer elements are pulled backwards, one by one. The abrasion forceexerted to the material to be transferred (kinetic friction) by thetransfer elements moving backwards is not able to pull the loadbackwards.

In FIG. 3 the width of the sides of the transfer trough is L1 and thewidth of the centre balk transporting solid material is L2. Suitablerelation of the widths is about 0.20-0.3. The load must differ from theloading of the apparatus of FIG. 2 in that sense that the friction forceformed on the centre balk 21 is smaller than the friction formed againstthe balks 13, 13′. The surface of the centre balk to be in contact withthe solid material is 21K, the surface of the movable side balks is 13Kand the surface of the immovable side plate to be in contact with thesolid material is 3K. The division of the friction and the exactdimensioning must be contemplated in accordance with patent WO 00/40383.

FIG. 4 shows simplified also a transfer apparatus in accordance with thepresent invention, said apparatus comprising sides 3 and 3′, fourmovable bottom balks 23, 23′, 24, 24′ supported on rolls 27. In thecentre portion of the apparatus there is an immovable, relatively narrowcentre balk 25 parallel to the transfer direction, collecting looserefuse material. The width of the friction surface 25K of the centrebalk is thereby less than a half of the width 24K of the frictionsurfaces of the balks on the sides. The construction in accordance withFIG. 4 is suitable for objects where a nearly non-littering bottom and aprominent climbing angle is required. In an apparatus cambered in thetransfer direction it is possible to use a narrow centre balk 25collecting refuse also with a transfer apparatus in accordance with FIG.3, comprising two movable transfer balks. An advantage thereby is aprominent transfer effect during the transfer motion.

Transfer device of FIG. 3 in accordance with the present inventioncomprised of two transfer balks is suitable for conditions where anuphill conveyor is not needed or where the climbing angle is relativelysmall. The operation of the device requires that the following twoequations are valid:Pe>Pz+Pg½Pe<Mu+P1.

The transferring force forward is composed of the friction force of twosurfaces 13K=Pe. The abrasion forces counteracting the transfer are thefriction Pk of the centre balk 21K and the friction 2P1 of the surfacesof the side plates. The common friction Pz is composed of these, inother words Pk+2P1=Pz.

In addition, the gravity of the earth counteracts or promotes thetransfer according to the climbing angle of the device. This isdescribed by force Pg (ascending +). The device transfers logs (or otherloose material mass), when two balks move forward, when Pe>Pz+Pg.

For pulling backwards the side balks an adequate internal friction ofthe mass to be transferred is essential, which in general is achievedwith an inclination of the side balks of about 45 degrees (and with anadequate loading h against the side-wall 3 (FIG. 3). This is caused bythe width of low-gradient portion 17 of the balks 13 that requires abigger load height h. By increasing the inclination of the balks 13, abigger linkage force can be achieved with logs and also with other kindof mass, but this is detrimental for the form of the conveyor.

The boundary friction Mu of a log bundle must be evaluated based onexperiments. In FIG. 2, the area of influence the boundary friction isindicated with a dashed line, and it has been shown in practice withpulpwood, that with a loading level in accordance with FIG. 2, theboundary friction is adequate and the log bundles travel coherently. Thelog bundle or the mass to be transferred travels forward when ½Pe<Mu+P1, because the mass to be transported does not move backwardtogether with the balks 13. With an inclining transfer apparatus, alsothe effect of the climbing angle must be taken into account.

Observations and experiments have shown, that with an apparatus of thepresent invention, tree trunks and other loose material can betransported, if the apparatus is loaded correctly and evenly.Applications of that kind are feeding of logs to a debarking drum andde-icing and heating of logs.

A prominent advantage with an embodiment of the transporting apparatusof the present invention is that there are only two movable balks thatcan also be implemented with slipper brackets. Another prominentadvantage is that as there are in that case only two parts to be pulledbackwards, the portion of the backward motion time is short and with atransfer apparatus in accordance with the invention, a considerablyhigher speed can be achieved.

In a conveyor for de-icing, washing or heating, the centre balk will beequipped with apertures of suitable size for drainage. In that case anadvantage is that the maintenance problem with rollers in especially wetconditions is solved. As an apparatus of the present invention also atransport apparatus must be considered, in which the side balks havebeen divided into two separate balks being equipped with their owndrives respectively. Thereby the conveyor can be used as a “two-balk”and as a four-balk conveyor with an immovable centre balk. An advantageof this kind of a conveyor is the higher top speed and if problemsoccur, the load can be transported so that the balks act in the returnmotion one by one.

Although in this description of the invention the operation of theapparatus has been mainly disclosed in connection with the transport ofpulpwood, the rules of the load balancing and of the packing forces arealso valid with small adjustments (according to experiments) with otherloose material.

1. A method for transferring tree trunks (9) or other loose material bymeans of a trough-shaped transfer apparatus by exerting abrasive forcesand friction forces to the material to be transferred on partialsurfaces of the transfer through, the abrasive forces actingsequentially in the transfer direction and in the return direction, andthe friction forces acting as braking forces, wherein the brakingfriction forces are exerted on at least three in respect to the transferdirection of the through transversally separate areas, and that theabrasive forces in the transfer direction are exerted to the material tobe transferred simultaneously on each areas (13) between the brakingfriction force areas (3, 3′; 21, 25), and that the abrasive forcesacting in the return direction are exerted non-simultaneously as wellwith respect to each other as to the abrasive forces in the transferdirection.
 2. A method in accordance with claim 1, wherein the abrasiveforce in return direction is exerted non-simultaneously on each of saidareas sequentially per area.
 3. An apparatus for transferring treetrunks (9) or other loose material, comprising a troughed transferapparatus, wherein the centre portion of the bottom of the apparatuscomprises a stationary balk (21) parallel with the trough, forming apart of the trough, and between the same and the stationary sides 3 and3′ both sided, a part of the trough is formed by balks (13, 13′) movableback and forth in the transfer direction and in the return direction. 4.An apparatus for transferring tree trunks (9) or other loose material,comprising a troughed transfer apparatus, wherein the centre portion ofthe bottom of the apparatus comprises a stationary balk (25) parallelwith the trough, forming a part of the trough, and between the same andthe stationary sides (3 and 3′) both sided there are two transfer balks(23, 24 and 23′, 24′) forming a part of the trough, movable back andforth in the transfer direction and in the return direction.
 5. Anapparatus in accordance with claim 3, wherein the width of the frictionsurface (25K) of the centre, stationary balk (25) is less than a half ofthe respective friction surface (24K) of the balk (24, 24′) adjacentthereto.
 6. An apparatus in accordance with claim 4, wherein the widthof the friction surface (25K) of the centre, stationary balk (25) isless than a half of the respective friction surface (24K) of the balk(24, 24′) adjacent thereto.